Method and apparatus for disposal of well flare gas in oil and gas drilling and recovery operations

ABSTRACT

A wellhead gas recovery system and method for the generation of power from wellhead gas is provided. A gas conduit is used to direct wellhead gas from a wellhead casing or wellhead bore to a stirling engine where the wellhead gas is used as the fuel source for the stirling engine. The wellhead gas is ignited and the burning wellhead gas is used as the heat source for the stirling engine. The thermal energy from the burning wellhead gas is converted transferred into motion by the stirling engine and the output of the stirling engine can be used to drive devices at the wellsite, generate electricity or other use.

This invention is in the field of wellhead gas recovery and more specifically generating power using wellhead gas collected as a by-product of oil collection.

BACKGROUND

Natural gas occurs in the collection of oil from an oil well, typically referred to as wellhead gas, because it concentrates at a wellhead during oil collection. Typically, this gas dealt with by either piping it to a collection system, shutting it in the well head, or in many cases venting or flaring it off.

Ideally, this gas is collected for later processing because the gas can often be processed into a saleable commodity. However, because many well sites are in relatively remote locations and the amount of gas collected is often relatively small, the requirements of collecting and transporting the gas for further processing is often uneconomical.

Raw wellhead gas (wellhead gas that has not been treated) typically comprises a mixture of methane, ethane, propane nitrogen carbon-dioxide, helium, and other compounds. In addition, the raw wellhead gas may contain small quantities of water vapor and/or significant amounts of hydrogen sulfide (H₂S) making the wellhead gas “sour gas”.

Wellhead gas with a hydrogen sulfide content exceeding 5.7 milligrams per meter of gas is typically considered to be “sour gas”. The pressure of the raw wellhead gas collected from the wellhead is typically 2 pounds per square inch (psi) or slightly higher, although the pressure of the raw wellhead gas leaving the wellhead can vary quite significantly.

One way of dealing with this wellhead gas produced as a by product of the oil recovery process at a well site, is to simply seal up the wellhead gas in the wellhead and prevent it from escaping into the atmosphere. However, by shutting the gas in the wellhead, the pressure in the well bore is increased and the production of oil from the well can be detrimentally affected because the flow of oil out of the well will often decrease as a result of the increased pressure created by the shut in gas.

The easiest solution to deal with this gas is to simply vent the gas to the atmosphere. To vent the gas, the wellhead gas is simply directed out of the wellhead casing and straight into the atmosphere. Venting the gas reduces the back pressure in the well bore, which can increase the production of the well as compared to shutting the gas in the well head. However, this vented gas, because of its composition contains many harmful elements and can be detrimental to the environment, especially if the gas is sour gas, and in many jurisdictions venting is strictly regulated, if allowed at all.

In an attempt to lessen some of the environmental problems associated with vented gas, the gas is often flared rather than vented (if the gas can support stable combustion). By flaring (or burning) the gas, the back pressure in the well head is reduced just as it is with venting, however, the flaring somewhat lessens the environmental problems that can occur with straight vented gas because the products of combustion of the gas are somewhat less harmful than the straight vented gas. For example, by burning the gas some of the hydrogen sulfide is converted to less harmful sulphur dioxide.

Although it is often not economically viable to collect and transport the gas to a location for further processing, the gas is still often a useful source of energy and it has been recognized that it is often desirable to recover some of the energy in the gas at the well site. Often these wellhead gases are of a sufficient quality to allow stable combustion (which is required for flaring) and these gases can be used as a fuel source. It is simply the economics of collection and transport that often makes it undesirable to attempt to collect these wellhead gases at a well site. Microturbines and other internal combustion engines or sometimes utilized to recover energy from these waste gases at the well site. Rather than simply venting or flaring the wellhead gas, the gas is directed to the microturbine or other combustion engine to serve as a fuel for the internal combustion engine. The power generated by the combustion engine using the wellhead gas as fuel can be used to power devices at the well site, generate electricity or any other suitable purpose.

However, using combustion engines to recover energy from wellhead gas is not without problems. The quality of the gas is often not ideal for use in a combustion engine and is often highly corrosive. Because of the corrosiveness of some of the gases, the combustion of these gases in an internal combustion often either quickly corrodes the internal components of the internal combustion engine requiring extensive maintenance and/or repair of the engines or the internal components of the internal combustion engine need to be made from high quality materials with very good corrosion resistance which are not highly susceptible to the corrosive gas. This makes it necessary for internal combustion engines using wellhead gas as a fuel to either be made from relatively costly high quality corrosion resistant materials or to have substantially shortened the service lives and/or require more regular and extensive maintenance if the internal combustion engines are made from more conventional materials.

In addition, internal combustion engines often require a relatively narrow range of air/fuel mixtures in order to operate, which can be hard to maintain with wellhead gas which may vary in supply and quality causing an internal combustion engine, fuelled with wellhead gas, to operate poorly or require extensive preconditioning of the wellhead gas in order to maintain an operable air/fuel mixture.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a system and method that overcomes problems in the prior an.

In a first embodiment of the invention, a wellhead gas recovery system for the generation of power is provided. The system comprises: a stirling engine, comprising a combustor and a gas conduit operative to route wellhead gas from a wellhead to the stirling engine. The system operates by routing wellhead gas the stirling engine and igniting the wellhead gas with a by the combustor and the ignited wellhead gas acts as a heat source to drive the stirling engine.

In a second embodiment of the invention, a wellhead gas recovery system for the generation of power is provided. The system comprises: a stirling engine, comprising a combustor; a gas conduit operative to route wellhead gas from a wellhead to the stirling engine, a compressor located inline on the gas conduit and operative to compress wellhead gas passing through the gas conduit to a predetermined pressure a pressure vessel located inline on the gas conduit and downstream from the compressor, the pressure vessel operative to store wellhead gas pressurized by the compressor; and a pressure regulator valve, located inline on the gas conduit and downstream from the pressure vessel, the pressure regulator valve operative to allow a regulated flow of pressurized wellhead gas at a predetermined pressure from the pressure vessel to the stirling engine. The system operates by routing wellhead gas the stirling engine and igniting the wellhead gas with a by the combustor and the ignited wellhead gas acts as a heat source to drive the stirling engine.

In a third embodiment of the invention, a wellhead gas recovery system for the generation of power is provided. The system comprises: a gas conduit operative to route wellhead gas from a wellhead to the stirling engine, a first stirling engine connectable to the gas conduit by a first pressure regulator valve; and second stirling engine connectable to the gas conduit. Wellhead gas is supplied to both the first stirling engine and the second sterling engine and the wellhead gas is ignited in the first stirling engine and second stirling engine to drive the first stirling engine and second stirling engine, respectively.

In fourth embodiment of the invention, a method of using a stirling engine to recover energy from wellhead gas is provided. The method comprises routing wellhead gas to a stirling engine; igniting the wellhead gas; and using the ignited wellhead gas as a heat source to drive the stirling engine.

The present invention provides a system and method wherein raw wellhead gas obtained as a by-product from an oil producing well is used as the fuel source for a stirling engine. The wellhead gas is typically collected from the wellhead during the pumping of oil at the well site, however, it could also be collected from the well bore during the drilling of the well bore. The wellhead gas is routed from the wellhead casing to a stirling engine where it is ignited by a combustor and used to drive the stirling engine. The power generated by the stirling energy can then be converted to either: kinetic energy, to provide mechanical power at the website for driving the oil pump and/or other mechanical devices: or electrical power, to power devices on the website or be fed back into an electrical grid.

In a stirling engine, heat is typically created by using a combustor to burn an incoming fuel. The heat generated by the burning fuel is then transferred to a working fluid circulated within the stirling engine and this working fluid undergoes a thermodynamic cycle, specifically a carnot cycle, and the thermal energy contained in the working fluid is converted into mechanical energy. This mechanical energy can be then be utilized to drive an output shaft, generate electricity, etc.

In contrast to an internal combustion engine where the combustion of the incoming fuel occurs inside the pistons of the engine, the combustion in a stirling engine occurs outside of the pistons. The working fluid inside the pistons and the internal workings of the stirling engine do not come into contact with the wellhead gas used as the fuel source and therefore the internal components of the stirling engine are not subjected to the corrosiveness of the wellhead gas. Because the internal components of the stirling engine do not come into contact with the corrosive wellhead gas, these internal components do not have to be made from high quality materials to prevent corrosion as a result of the combusting wellhead gas and can have a substantially extended service life, relative to internal combustion engines, using materials of lower quality.

In addition, the fuel supply does not need to be as exact as it does for an internal combustion engine. Unlike internal combustion engines that often require a relatively narrow range of air/fuel mixture in order to operate, stirling engines only require the incoming fuel to be able to maintain a relatively stable combustion because the incoming fuel is merely ignited to provide heat to the stirling engine. Minor fluctations in the heat output from the burning fuel typically do not significantly affect the operation of the stirling engine. The air/fuel mixture, pressure, and other variable in the fuel supply do not have to be regulated as strictly as in an internal combustion engine making the operation of the stirling engine on the wellhead gas more reliable because fluctuations in the composition and supply of the wellhead gas to the stirling engine will not have as detrimental an effect as these fluctuations would have on an internal combustion engine.

Even though many stirling engines typically have combustion chambers in which the fuelling source is combusted, these combustion chambers need to merely contain the combustion of the fuel while the heat of the combustion is being transferred to the stirling engine and do not contain any moving parts. Therefore, the combustion chambers in stirling engines do not need to have the same tolerances that combustion chambers in internal combustion chambers require. The combustion chambers themselves can be made of more corrosive resistant materials or be more frequently replaced without having to tear down and rebuild the entire stirling engine.

In addition, by burning the wellhead gas, some of the hydrogen sulfide which is very harmful and may be present in the wellhead gas is converted into less harmful sulfur dioxide. Because the stirling engine will allow a much wider operating range for the ignited wellhead gas, the air/fuel mixture and temperate can be optimized to try to enhance the conversion of the hydrogen sulfide to sulfur dioxide; allowing more hydrogen sulfide in the wellhead gas to be converted to sulfur dioxide.

In a further embodiment, a system and method is provided for allowing a stirling engine to be fueled by wellhead gas where the supply of wellhead gas from the wellhead is relatively unstable. In this embodiment, the raw wellhead gas is directed to a compressor where the wellhead gas is compressed and stored in a pressure vessel. A pressure regulator valve allows a steady flow of wellhead gas from the pressure vessel to the sterling engine, where the wellhead gas is ignited to supply heat to drive the stirling engine.

In this manner, when the raw wellhead gas from the wellhead drops below a suitable pressure, the compressed wellhead gas stored in the pressure vessel can compensate for the reduce pressure in the supply or raw wellhead gas from the wellhead. The length of time that this system can compensate for a fluctuating supply of raw wellhead gas will vary depending on the amount of compression of the wellhead gas, the size of the pressure vessel and the pressure level allowed by the pressure regulator valve.

In a further embodiment, two or more- stirling engines are supplied with raw wellhead gas for situations where the pressure of the raw wellhead gas is sufficient to supply fuel to more than one stirling engine. The stirling engines are connected to a gas conduit in series with pressure regulating valves regulating the supply of the wellhead gas in the gas conduit to each of the stirling engines. In this manner, well sites that produce substantial amounts of wellhead gas can be used as the fuel source for multiple stirling engines.

DESCRIPTION OF THE DRAWINGS

While the invention is claimed in the concluding portions hereof, preferred embodiments are provided in the accompanying detailed description which may be best understood in conjunction with the accompanying diagrams where like parts in each of the several diagrams are labeled with like numbers, and where:

FIG. 1 is schematic diagram of a system for recovering energy from wellhead gas, in accordance with the present invention;

FIG. 2 is a schematic diagram of a stirling engine in accordance with the present invention, connected to an output shaft;

FIG. 3 is a schematic diagram of a stirling engine, in accordance with the present invention connected to an electrical generator, supplying electrical power to a power grid;

FIG. 4 is a schematic diagram of a further embodiment of a system in accordance with the present invention comprising a compressor and a pressure vessel; and

FIG. 5 is a schematic diagram of a further embodiment of a system in accordance with the present invention wherein a plurality of stirling engines are fueled with wellhead gas.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 is a schematic illustration of a system 10 for recovering energy from wellhead gas. The energy recovery system 10 comprises a gas conduit 25 and a stirling engine 30. The gas conduit 25 transfers raw wellhead gas, collected as a by-product from oil producing wells, from a wellhead 20 to the stirling engine 30.

The raw wellhead gas is collected from the top of the wellhead as is known in the art and typically comprises a mixture of methane, ethane, propane, nitrogen, carbon-dioxide, helium, and other compounds. In addition, the raw wellhead gas may contain small quantities of water vapor and/or significant amounts of hydrogen sulfide (H₂S) making the wellhead gas “sour gas”. Typically, wellhead gas with a hydrogen sulfide content exceeding 5.7 milligrams per meter of gas is typically considered to he “sour gas”. The pressure of the raw wellhead gas collected from the wellhead is typically 2 psi or slightly higher allowing the raw wellhead gas to move through the gas conduit 25 without requiring additional compression, although the pressure of the raw wellhead gas leaving the wellhead can vary quite significantly.

The stirling engine 30 is a stirling engine as is conventionally known and could have various configuration, however, stirling engine 30 typically comprises: at least one combustion chamber 32; a combustor 33; one or more pistons 34; a heater portion 35; typically a regenerator 36; a cooling portion 37 and a power collecting unit 38. Although the stirling engine 30 is illustrated as a beta configuration stirling engine, stirling engine 30 could be any type of configuration, as is know for stirling engines, including alpha, beta, gamma, rinia alpha configuration or other stirling engine configuration.

In operation, the raw wellhead gas is transferred from wellhead (not shown) through the gas conduit 25 and into the combustion chamber 32 of the stirling engine 30. Once the wellhead gas enters the combustion chamber 32, the raw wellhead gas is ignited by the combustor 33. This ignited wellhead gas is used as the heat source for the stirling engine 30.

Typically, the wellhead gas will be collected from a wellhead casing (not shown) as a by-product of the collection of oil from the well, however, wellhead gas can also be released during the drilling and preparation of the well for the production process and wellhead gas collected during the drilling and/or preparation of the well could also be used and supplied through the gas conduit 25 to the combustion chamber 32 where it is ignited and used as the heat source to drive the stirling engine 30.

As is typical for stirling engines, the heat source is used to transfer thermial energy to a heating portion 35 containing a working fluid. Wellhead gas, ignited in the combustion chamber 32 by the combustor 33, forms the heat source and a portion of the thermal energy released by the burning of the wellhead gas is transferred to working fluid in the heating portion 35 of the stirling engine 30. The heated working fluid then drives the pistons 34 and the working fluid is then recirculated through the cooling portion 37. Although the stirling engine 30 in FIG. 1 is illustrated with a single piston 34, it is known by those skilled in the art that some configurations of stirling engines contain multiple piston arrangements and stirling engines with more than one piston could be used in the present invention.

Although it is not necessary for a stirling engine to comprises a regenerator 36, many do to improve their operation, such as sterling engines in the beta configuration and a stirling engine 30 may be used that does not have a regenerator 36.

The fluid in the heating portion 35, cooling portion 37 and piston 34 is not in fluid communication with the combustion chamber 32 so the corrosive wellhead gas being ignited by the sterling engine 30 does not to affect the internal workings of the pistons 34 of the stirling engine 30 and no combustion of gases occurs in the pistons 34 or any other part of the stirling engine 30, with the exception of the combustion chamber 32.

The stirling engine 30 is driven by the heat source created by the ignited wellhead gas and the output of the stirling engine is harnessed by the power collecting unit 38. FIG. 2 illustrates a stirling engine 30, in accordance with the present invention, where the displacement of the piston 34 is harnessed mechanical energy, such as by rotating a output shaft using a rombic drive 39, although other devices could be used to harness the mechanical power such as a swash plate drive (not shown).

FIG. 3 illustrates a stirling engine 30, in accordance with the present invention, wherein the displacement of the piston 34 is harnessed to drive a generator 40 and output electrical energy. The generator 40 introduces a load in the form of a linear alternator coils 42, wherein the passing of magnets 44 past the linear alternator coils 42 create an electrical current. This electrical current can then be used either to power devices onsite or, as shown in FIG. 3, processed through a transformer 50 and connected to an electrical grid 55, to pass the electrical energy back to the electrical grid 55.

FIG. 4 illustrates a further embodiment of the present invention, for use when the supply of wellhead gas is relatively unsteady. Energy recovery system 100 comprises: a gas conduit 25, a compressor 110; a pressure vessel 115; a pressure regulator valve 120; and a stirling engine 30.

Some oil producing wells may produce a relatively unsteady supply of raw wellhead gas, wherein the pressure of the wellhead gas exiting the wellhead casing can fluctuate substantially. The supply of raw wellhead gas can fluctuate from pressures above 2 psi to much lower; so low that the raw wellhead gas will not move through the gas conduit 25 or allow adequate combustion by a combustor (not shown) of the stirling engine 30.

The raw wellhead gas is transported from the well head or well bore (not shown) through the gas conduit 25 to the compressor 110. The compressor 110 compresses the wellhead gas to a higher pressure and passes the pressurized wellhead gas to the pressure vessel.

A pressure regulator valve 120 is provided in proximity to the exit of the pressure vessel 115 to allow wellhead gas at a predetermined pressure to be transported into a combustion chamber (not shown) of the stirling engine 30, where the compressed wellhead gas is ignited to drive the stirling engine 30 and the power generated by the stirling engine 30 can be harnessed, as described above.

Using the power recovery system 100, raw wellhead gas can be used when the raw wellhead gas is supplied at a relatively unsteady rate. The pressure vessel 115 stores compressed wellhead gas so the supply of wellhead gas to the stirling engine 30 is regulated. The size of the pressure vessel 115, tie pressure the wellhead gas is compressed to by the compressor 110 and/or the settings of the pressure regulator valve 120 will determine the amount of time the stirling engine 30 can be supplied with a sufficient flow of wellhead gas when the raw wellhead gas supplied from a wellhead (not shown) drops below a suitable pressure.

FIG. 5 illustrates a further embodiment of the present invention, wherein the pressure of the raw wellhead gas is greater than required for the operation of a single stirling engine 30. System 200 comprises a gas conduit 25; a first pressure regulator valve 210; a first stirling engine 30A; a second pressure regulator valve 220; and a second stirling engine 30B.

Wellhead gas is supplied to the first stirling engine 30A and second stirling engine 30B by the gas conduit 25. The first pressure regulator valve 210 controls the flow of wellhead gas to the first stirling engine 30A. The remaining flow of wellhead gas that does not pass through the first pressure regulator valve 210 will flow through the second regulator valve 220 and to the second stirling engine 30B. In this manner, wellhead gas can be supplied to multiple stirling engines 30A and 30B and multiple stirling engines 30A and 30B can he used to generate power using the wellhead gas as fuel.

Although FIG. 5 illustrates two stirling engines 30A and 30B, it will be apparent to a person skilled in the art that more than two stirling engines could be used in the same manner providing the supply of wellhead gas is sufficient to fuel the additional stirling engines.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous changes and modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact constriction and operation shown and described, and accordingly, all such suitable changes or modifications in structure or operation which may be resorted to are intended to fall within the scope of the claimed invention. 

1. A wellhead gas recovery system for the generation of power, the system comprising: a stirling engine, comprising a combustor; and a gas conduit operative to route wellhead gas from a wellhead to the stirling engine, wherein the wellhead gas routed to the stirling engine is ignited by the combustor and the ignited wellhead gas acts as a heat source to drive the stirling engine.
 2. The system of claim 1 wherein the stirling engine comprises at least one combustion chamber and wellhead gas is directed to the at least one combustion chamber by the gas conduit and the wellhead gas is ignited in the at least one combustion chamber by the combustor.
 3. The system of claim 2 wherein the at least one combustion chamber is operably removable whereby the at least one combustion clamber can be removed and replaced when the at least one combustion chamber becomes corroded from the wellhead gas.
 4. The system of claim 2 wherein the at least one combustion chamber comprises a corrosion resistant material.
 5. The system of claim 1 wherein power generated by the stirling engine is used to drive an output shaft.
 6. The system of claim 1 wherein power generated by the stirling engine is used to drive an electrical generator to output electrical energy.
 7. The system of claim 6 wherein the electrical generator is operatively connected to an electrical power grid and wherein electrical energy produced by the electrical generator is supplied to the electrical power grid.
 8. The system of claim 1 further comprising: a compressor located inline on the gas conduit and operative to compress wellhead gas passing through the gas conduit to a predetermined pressure; a pressure vessel located inline on the gas conduit and downstream from the compressor, the pressure vessel operative to store wellhead gas pressurized by the compressor; and a pressure regulator valve, located inline on the gas conduit and downstream from the pressure vessel, the pressure regulator valve operative to allow a regulated flow of pressurized wellhead gas at a predetermined pressure from the pressure vessel to the stirling engine.
 9. The system of claim 1 comprising: a first stirling engine connectable to the gas conduit by a first pressure regulator valve; and a second stirling engine connectable to the gas conduit, wherein wellhead gas is supplied to both the first stirling engine and the second sterling engine and wherein wellhead gas is ignited in the first stirling engine and second stirling engine to drive the first stirling engine and second stirling engine, respectively.
 10. A method of using a stirling engine to recover energy from wellhead gas, the method comprising: routing wellhead gas to a stirling engine; igniting the wellhead gas; using the ignited wellhead gas as a heat source to drive the stirling engine.
 11. The method of claim 10 wherein the wellhead gas is directed to at least one combustion chamber of the stirling engine and ignited in the at least one combustion chamber.
 12. The method of claim 11 comprising replacing the at least one combustion chamber when the at least one combustion chamber has become corroded.
 13. The method of claim 11 wherein the at least one combustion chamber comprises a corrosion resistant material.
 14. The method of claim 10 comprising using power generated by the stirling engine to drive an output shaft.
 15. The method of claim 10 comprising using power generated by the stirling engine to generate electricity.
 16. The method of claim 15 wherein the electricity generated by the stirling engine is supplied to an electrical grid. 